The present invention generally relates to an apparatus for semiconductor processing and more specifically, to an improved substrate cleaning apparatus.
As used herein, semiconductor substrate processing includes but is not limited to the processing of carriers, sliders, wafers, disk heads, disks, squares, rounds, reticles and flat panel displays. At one or more stages of processing a semiconductor substrate, as indicated above, it is often necessary to clean the substrate, and various machines for cleaning substrates are known in which the substrates are cleaned by ultrasonic, megasonic or gigasonic energy, low, medium or high pressure water at various temperatures, brushes, either fixed or rotating, or other means. Further, the substrate is supported in either a vertical or horizontal orientation during the cleaning process. The cleaning process may be implemented while the substrate is either at a fixed position or moving with respect to one or more cleaning devices. If at a fixed position, the substrate is either stationary or rotating, and cleaning devices, for example, brushes, are most often rotating although nonrotating brushes may also be used.
Of particular importance in maintaining the integrity of the cleaning process is providing a desired pressure or force between the brush and the substrate during the cleaning process. If there is too little brush pressure or force, an inferior cleaning action is produced; and the quality of the cleaning process is poor. However, with too great a brush force on the substrate, the brush medium, for example, bristles, may bend or deflect to such an extent that the brush action is less effective or can cause substrate damage, thereby providing a lower quality cleaning process. In other situations, the brush medium may be deflected into the core of the brush and release contaminants onto the substrate. That action is obviously counterproductive to a high quality substrate cleaning process.
In order to provide a consistent substrate cleaning process, several devices are known for providing a proper brush force. With one device, a drive, for example, a pneumatic cylinder, moves a brush assembly downward into contact with the substrate until the brush assembly contacts a positive stop. Thus, with the brush assembly at a known and repeatable position with each substrate, a consistent brush force is applied to each substrate. This device does not provide a particularly constant brush force and is not sensitive to changing conditions that affect brush force, such as brush wear, substrate thickness, brush medium diameter differences, stop wear, or brush core diameters. Further, such a device is difficult to accurately readjust with different size brushes and substrates.
With another device a rotating, horizontally oriented brush is mounted on a vertical slide. A counterweight is used to balance the brush assembly at a desired height such that the brush is immediately above or just touching the substrate. A cylinder is then used to move the brush assembly downward, and air pressure in the cylinder is used to provide a desired brush force onto the substrate. A device of this nature is very complex and is very difficult to maintain in a calibrated balanced condition. Further, the device is also difficult to adjust to accommodate different size substrates and different brushes. Further, this other device requires a relatively large number of components to implement and thus, is very expensive.
There are other cleaning devices in which the brush is moved through precise increments of motion and into contact with the substrate against the action of a mechanical spring. The force of the brush against the substrate is a function of the extent to which the spring is compressed. While this system is simpler than some other systems, it is also difficult to adjust for different size substrates and is also subject to inconsistencies caused by variations in the spring constant of the spring.
In another system, a substrate is supported vertically and a brush extending over a diameter of the substrate is suspended at its upper end from one end of a horizontally extending drive arm. The opposite end of the drive arm is connected to a cylinder which reciprocates the drive arm and the brush in a horizontal direction into and out of contact with the wafer. A force transducer is located at the opposite end of the drive arm and is used to control the force that the cylinder applies to the opposite end of the drive arm, thereby controlling the force that the brush applies to the substrate. This system has an advantage over prior systems in that a force used to move the brush into contact with the substrate is measured and fed back to a control, thereby providing a real time control over the force applied by the cylinder during the cleaning process. Thus, the system has the advantage of being able to provide a more consistent force during the cleaning process than the prior systems. Further, the desired or target brush cleaning force is more easily changed to accommodate different size substrates and brushes than was possible with other systems described above. However, such a system has several disadvantages. First, while the force being measured is directly related to the force being applied to the substrate, it is not a measure of the force being experienced by the substrate. The substrate is vertically suspended as are the brushes and both are subject to some deflection over their length as is the drive arm. Thus, the force on the substrate is subject to some variation over that measured at the opposite end of the drive arm. Further, the device has a further complexity in that the motion of both the substrate and the brushes must be precisely controlled.
Therefore, there is a need for an improved substrate cleaning machine that has the ability to precisely control the force being applied by a cleaning brush and also be of a reliable and cost efficient design.
The present invention provides a substrate cleaning apparatus having a more efficient and reliable cleaning process. The cleaning apparatus of the present invention further provides a more consistent, reliable and higher quality substrate cleaning process that has a relatively simple and inexpensive structure.
In accordance with the principles of the present invention and the described embodiments, the substrate cleaning apparatus of the present invention includes a vertically extending spindle having a substrate supported on its upper end. A brush extends generally horizontally over the substrate, and a force measuring gage is mounted to the spindle for detecting forces applied to the substrate. A spindle control is electrically connected to the force measuring gage and mechanically coupled to the spindle and causes the spindle to move as a function of the forces being applied to the substrate by the brush. The substrate cleaning apparatus of the present invention has the advantage of providing the user with a relatively simple and less expensive apparatus that provides a consistent high quality substrate cleaning process.
In another embodiment, the present invention includes a method of cleaning a substrate supported on an upper end of a spindle by first positioning a brush at a fixed elevation over the substrate. Next, the spindle is moved upward to bring the substrate into contact with the brush. Thereafter, a cleaning force on the substrate caused by the brush is measured, and the spindle is moved in response to the measured cleaning force on the substrate.
In one aspect of the invention, the substrate is first moved into contact with the brush; and thereafter, the substrate is moved upward through an incremental displacement into a cleaning contact with the brush. In another aspect of the invention, a user provides a cleaning force value and a tolerance bandwidth around that value, thereby defining a range of acceptable cleaning forces. the spindle is moved to maintain the cleaning force on the substrate within the range of acceptable cleaning forces. In a still further aspect of the invention, an acceptable-cleaning force value is provided, the spindle-is moved to maintain the cleaning force on the substrate substantially equal to the cleaning force value.